Throughout this application various publications are referenced by the names of the authors and the year of publication within parentheses. Full citations for these publications may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.
Heat shock genes are activated in the response of a cell to stress, such as an increase in temperature or exposure to inhibitors of oxidative phosphorylation (1). The heat shock response involves the immediate activation of several heat shock genes, resulting in extensive synthesis of several heat shock proteins (Hsp's), plus a rapid decrease of transcription of most other genes and a cessation of most other protein synthesis (for review refs. 1, 2). In many organisms heat shock related genes are expressed during cell development For instance heat shock genes are expressed specifically in mice during early embryogenesis (3), in erythropoesis (4), and at sporulation in yeast (5). The role of the heat shock gene response in these cases is unclear but t indicates that heat shock proteins, which have a nuclear location (6, 7) may be involved in differentiation.
Many parasitic protozoa have life cycles that involve an insect vector and a mammalian host. Adaption of the protozoa to either of its hosts involves differentiation accompanied by extensive morphological alterations, often including a sexual life cycle in the insect vector and a switch from oxidative phosphorylation in the insect to anaerobic respiration in the mammalian host (8). Trypanosoma brucei in addition has been shown to lose its protective cell surface coat when entering the fly gut where it differentiates into the non-infective procyclic trypanosome (9, 10). This cell surface coat is re-expressed in the infective metacyclic trypanosomes that are found in the insect salivary glands (10). Here we show that differentiation of the Kinetoplastid protozoa Trypanosoma brucei and Leishmania tropica major, involves a heat shock response. Insect vectors like the sandfly and the tsetse fly (transmitting L.t. major and T. brucei, respectively) are restricted to habitats with a very narrow temperature range from 22.degree. C. to 28.degree. C. (11, 12). In vivo, transfer of the parasite from its non-temperature regulated (poikilothermic) insect vector to the homeothermic mammalian host will therefore trigger this heat shock response. In vitro this response can be mimicked by a temperature increase (25.degree. C. to 37.degree. C.) which results in differentiation similar to that which occurs in vivo.